In the printed circuit board industry where spindles are employed for drilling or routing circuit boards, a drawbar secures a collet within which the drill or router bit is secured. A very strong spring is positioned within the spindle and applies sufficient force on the order of 400 to 800 pounds to secure the drill or router bit in the collet. This large amount of force is required to properly secure the tool bit and maintain its operational characteristics while the spindle is rotating at speeds as high as 350,000 RPM or greater, but may be operated at speeds as low as 2,000 RPM. The spindle structure may drive a drill as small as 4 mils in diameter or as large as ¼ of an inch in diameter. During operation, the drill or router bit must be changed from time to time and when such change occurs, a force must be applied to the drawbar sufficient to overcome the 400 to 800 pounds of axial force being applied by the spring.
In the prior art such high forces were obtained by using air pressure at approximately 400 pounds (PSIG) which was obtained by increasing shop air pressure which is approximately 65 to 125 PSIG and intensifying it. The machines, used for intensifying this air pressure are complicated pneumatic mechanical piston devices which are very noisy, unreliable and extremely expensive to maintain. As an alternative and where space permits a multitude of pistons or diaphragms may be arranged and employed in such spindles to overcome the force of the spring to release the tools. The utilization of such pistons and diaphragms causes the spindle to become quite long and heavy. Since these spindles in the printed circuit board industry produce many holes per minute, the spindle weight is important form an inertia standpoint. A need, therefore, exists for an actuating mechanism which is lower in weight and does not increase the size of the spindle and yet which will exert sufficient force to overcome the spring force to actuate the collet and release the tool being held by the collet.